The present invention generally relates to magnesium-based casting alloys having improved elevated temperature properties and more particularlyrelates to magnesium-aluminum-strontium-calcium alloys having improved creep resistance and tensile yield strength, particularly at elevated temperatures of at least 150xc2x0 C., and good salt-spray corrosion resistance.
Magnesium-based alloys have been widely used as cast parts in the aerospace and automotive industries and are mainly based on the following four systems:
Mgxe2x80x94Al system (i.e., AM20, AM50, AM60);
Mgxe2x80x94Alxe2x80x94Zn system (i.e., AZ91D);
Mgxe2x80x94Alxe2x80x94Si system (i.e., AS21, AS41); and
Mgxe2x80x94Al-Rare Earth system (i.e., AE41, AE42).
Magnesium-based alloy cast parts can be produced by conventional casting methods which include diecasting, sand casting, permanentand semi-permanent mold casting, plaster-mold casting and investment casting.
These materials demonstrate a number of particularly advantageous properties that have prompted an increased demand for magnesium-based alloy cast parts in the automotive industry. These properties include low density, high strength-to-weight ratio, good castability, easy machineability and good damping characteristics.
AM and AZ alloys, however, are limited to low-temperature applications because they are known to lose their creep resistance at temperatures above 150xc2x0 C. AS and AE alloys, while developed for higher temperature applications, offer only a small improvement in creep resistance and/or are expensive.
It is therefore an object of the present invention to provide relatively low cost magnesium-based alloys with improved elevated-temperature properties.
It is a more particular object to provide relatively low cost magnesium-aluminum-strontium-calcium alloys with good creep resistance and tensile yield strength, particularly at elevated temperatures of at least 150xc2x0 C., and good salt-spray corrosion resistance.
The present invention therefore provides a magnesium-based casting alloy that comprises: 1 to 12% by weight (wt.) aluminum; 0.1 to 0.6% by wt. strontium; and 0.1 to 0.5% by wt. calcium, with the balance being magnesium except for impurities commonly found in magnesium alloys.